Folding containers are conventionally known which are composed of long side walls connected, via hinge members, to respective opposite long side portions of a bottom portion formed so as to have a rectangular planar shape and short side walls also connected, via hinge members, to respective opposite short side portions of the bottom portion. The long side walls and the short side walls are set up perpendicularly to the bottom portion to assemble the side walls and the bottom portion into a box form. Furthermore, when the folding container is folded, the long side walls and the short side walls are folded so as to lie on top of the bottom portion. With the folding container assembled into the box form, the long side walls and the short side walls are locked by lock members so as to prevent the long side walls or the short side walls from falling down toward the bottom portion.
By way of example, the Unexamined Japanese Patent Application Publication (Tokkai) No. 2003-40263 discloses a folding container in which a locking operation and an unlocking operation are performed as follows. An operation portion of a lock member disposed on each short side wall is moved in a vertical direction. Furthermore, the vertical movement of the operation portion is converted into horizontal movement via an appropriate mechanism such as a link mechanism to move a bar-like member to move in a horizontal direction. The tip of the bar-like member is thus inserted into or removed from an engaging portion formed in a corresponding long side wall. Consequently, the long side walls and the short side walls are locked or unlocked so as to prevent the short side walls from falling down toward a bottom portion.
According to the above-described conventional folding container, to fold the folding container assembled into the box form, an operator pushes the operation portion downward. However, depending on a position where the operator pushes the operation portion downward, the operation portion may be tilted during the downward movement instead of being moved downward in a horizontal state. Where the operation portion is tilted during the downward movement, the paired bar-like members positioned on the right and left of the operation portion vary in projection amount or retraction amount. This disadvantageously results in an unreliable unlocking operation.
Furthermore, the vertical movement of the operation portion is converted into the horizontal movement of the bar-like members via a complicated mechanism. Thus, a heavy transmission loss is involved in the conversion of the vertical movement of the operation portion into the horizontal movement of the bar-like members. Thus, a strong force is required to move the operation portion in the vertical direction, hindering a quick unlocking operation.